John G. Berberian, Ph.D.

Dr. Berberian earned his undergraduate degree at the University of Massachusetts and his Ph.D. at Brown University. His area of research is Chemical Physics and his particular interest is the structure of liquids. Dr. Berberian came to Saint Joseph's University's Chemistry Department in 1973 after spending 4 years in the Biomedical Engineering Graduate Group at the Moore School of Electrical Engineering at the University of Pennsylvania. In April 1994, he was given a joint appointment as Professor of Chemistry and Physics. His research has been supported by The Research Corporation, The Petroleum Research Fund, and the National Science Foundation. His research involves low temperature dielectric and static viscosity measurements (100K to 200K) on supercooled liquids.

Research

Molecular motions in dielectric liquids

My area of research is the study of the structure of liquids, in particular, molecular motions in the liquid state. Fundamentally, my research deals with the correlation of molecular rotational motion with liquid properties. Dielectric spectroscopy is the mainstay experimental method used in my laboratory to measure molecular rotational motion. Static viscosity measurements complement the dielectric data, and heat capacity measurements are proposed for future measurements.

Of particular interest in our research is the wide range of time scales and temperatures involved in the measurements for the particular exemplary system used in our study. The particular system used for study is 3-bromopentane, a symmetric molecule with a dipole moment in the middle transverse to the molecular axis. This molecule is the simplest polar molecular system that will readily supercool to yield a wide range of temperatures over which the sample remains in its liquid state.

We are interested in the rate of molecular rotation of the dipole. The time scale for the rotation for a small molecule such as 3-bromopentane is in the picosecond range at room temperature and in the kilosecond range at 105K (-178 degrees Celsius). This wide range of times is covered by several measurement techniques: time domain spectroscopy (picoseconds to microseconds), admittance bridges (microseconds to 10's of seconds), and transient measurements (milliseconds to hours). The wide range of temperature used (298K to 100K) presents an additional experimental challenge for both measurement and control. A new direction in the research is the study of molecular rotation of 3-bromopentane in mixtures with its non-polar homologue, 3-methylpentane, the bromo group being approximately the same size as the methyl group. We will be looking at the rotation of the polar moiety of the mixture as the number density of the polar moiety decreases.